Automatic control for return motion of cutoff saw head

ABSTRACT

A lever mounted on the cutting head of a cutoff saw has a feeler arm that normally extends across the path of stock feed, parallel to the cutting edge of the blade to engage the stock in position to be cut and, by its disengagement from the stock as the cutting head is raised after the cut is completed, it trips a switch and prevents further elevation of the head. When the cutting head is so positioned that advancing stock can strike it, the feeler, by engagement with the stock, is displaced from its normal position, and trips another switch to effect elevation of the head and prevent stock feed advance.

United States Patent [191 Robinson et ai.

[ll] 3,72Ll39 [451March 20, 1973 [s41 AUTOMATIC CONTROL FOR RETURN MOTION 0F CUTOFF SAW HEAD both of Savage, Minn.

[73] Assignee: Continental Machines, lnc., Savage,

Minn. 22 Filed: July 19,1971

[2|] App|.N0.: 163,612

301. Foreign Application Priority 0m Sept. 1,1970 Great Britain ..41,7s9/70 521' U.S.Cl "1.83/63, 83/201,83/248, p n j 83/360,83/365,83/527 511 Int. Cl. ..B23d 55/00 [58] ,Fiel'dof Search. ...83/63, 201,248, 360, 365,

Inventors: Le Roy E. RobinsomLeslle J. Pellz,

[56] References Cited UNITED STATES PATENTS 3,386,322 6/1968 Stone et al ..83/527 X Primary Exam'iner-A-James M- Meister Attorney-Ira Milton Jones 571 ABSTRACT A lever mounted on the cutting head of a cutoff saw has a feeler arm that normally extends across the path .of stock feed, parallel to the cutting edge of the blade to engage the stock in position to be cut and, by its disengagement from the stock as the cutting head is raised after the cut is completed, it trips a switch and prevents further elevation of the head. When thecutting head is so positioned that advancing stock can strike it, the feeler, by engagement with the stock, is displaced from its normal position, and trips another switch to effect elevation of the head and prevent stock feed advance. I

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lNvENToRs LaEuyEEabmsan LESZIE JFEZZZ BY' AT-r Nev AUTOMATIC CONTROL FOR RETURN MOTION OF CUTOFF SAW HEAD This invention relates to cutoff saws, which are employed for cutting long lengths of stock into shorter pieces and which have a cutting head that is power actuated in its cutting and return movements; and the invention is more particularly concerned with means for effecting automatic control of the return motion of the cutting head of such a saw.

The most popular and efficient cutoff saws are those in which an endless saw band is trained around a pair of pulleys or band wheels, generally in the manner of a band saw. Such a machine comprises a base or bed that provides an elongated feed table along which stock to be out can be advanced to bring it to a cutting zone, and a cutting head mounted on the machine base at the cutting zone for reciprocating movement in cutting and return strokes. In an endless band cutoff saw the cutting head comprises the band wheels, the endless blade trained around them, and suitable structure by which the band wheels are rotatably supported and which is mounted on the machine base for reciproca tion. In some cutoff machines the cutting head reciprocates with a translatory motion (horizontally in some cases, vertically in others) while in other machines it swings scissors fashion; but in every instance its reciprocatory motion carries it across a path of stock advance defined by the feed table. In all cutoff saws of the band type, the cutting head is actuated in its cutting and return strokes by power drive means.

In some such machines the stock to be cut is manually pushed along the feed table, which normally comprises a set of rollers upon which the stock is supported. In the more sophisticated cutoff saws, power driven stock indexing means advance the stock towards and through the cutting zone, stopping it for a cut each time a preset increment of advance has been obtained.

Usually the power driven indexing means comprises a carriage which is mounted on the machine base for reciprocation along the path of stock movement and which comprises a vise that grips the stock when the carriage is in a retracted position. After the carriage has advanced the stock, the stock is gripped for cutting by a stationary vise located adjacent to the cutting zone. Control means for the machine, associated with the actuators for the cutting head, the carriage and the vises, synchronize and coordinate their movements.

In earlier cutoff saws that had automatic stock feed, the control means for the machine caused the cutting head to be moved all the way back to a defined retracted position before the stock feeding carriage was permitted to begin its advancing movement. It was recognized that such full range movement of the cutting head in each cutting cycle involved a waste of time whenever stock was being cut that was of less than the maximum size for which the machine was designed. Unnecessary delay occurred not only during retracting movement of the cutting head beyond the point at which it was clear of the stock, but also during the subsequent cutting stroke of the head, prior to actual cutting engagement with the stock.

To overcome this inefficiency and speed up the cutting cycle, later cutoff saws were equipped with manually adjustable trip switches that could be set to limit the return motion of the cutting head to only that which was needed to clear the stock. While theoretically efficient, this expedient was subject to human error. If the operator did not properly adjust the trip switch for the size of stock to be cut, or if the stock was of varying thickness along its length and the trip switch was set for its thinner portions, the stock could collide with the cutting head, often with consequent damage to the saw blade. And of course adjustment of the trip switch, while not necessarily difficult, was nevertheless an operation that required some time and skill as well as attention.

With the above stated considerations in mind, it is the general object of this invention to provide means for automatically so controlling the return stroke of the cutting head of a cutoff saw as to assure that the head will always be clear of the advancing stock, even if the stock has substantial variations in thickness along its length, but to nevertheless move the cutting head in the return direction only just enough to provide such clearance.

It is also a general object of this invention to provide automatic sensing means for controlling the return stroke of the cutting head in a power cutoff saw, which sensing means is responsive to the presence of stock to be cut in or near the cutting zone and eliminates the need for any human attention or intervention in order to attain the minimum possible cycle time in the operation of the machine.

The invention is herein described with reference to the type of cutoff saw having an endless band as its cutting tool, inasmuch as the superior cutting efficiency of such a machine makes any delay in the non-cutting portion of its cycle particularly significant, but it will be appreciated that the invention is applicable to cutoff saws of all types and can be employed to advantage on any cutoff saw.

In those band-type cutoff machines in which the cutting head moves with a horizontal translatory motion in its cutting and return strokes, the head is usually tiltingly adjustable to either side of vertical so that the plane of its out can be oblique to the longitudinal axis of the stock. It is among the objects of this invention to provide an automatic control of the above described character that is applicable to such cutoff saws as well as to cutoff machines of other types.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate several complete examples of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a perspective view of a cutoff saw equipped with the control system of this invention;

FIG. 2 is a perspective view of the work sensing finger or feeler that forms an essential part of the control system, and the adjacent portion of the machine;

FIG. 3 is a front elevation view of the work sensing finger and its associated structure, parts of which are broken away;

FIG. 4 is a sectional view through FIG. 3 on the plane ofthe line 4-4;

FIG. 5 is a sectional view through FIG. 3 on the plane of the line 55;

FIGS. 6, 7 and 8 are diagrammatic front views of the machine illustrating how the presence of work in the cutting zone is utilized through the work sensing finger to actuate the control;

FIG. 9 is a diagrammatic top view of a portion of the machine illustrating how unintended advance of the work actuates the work sensing finger;

FIG. 10 is a block diagram of the entire control system; and

FIG. 11 is a more or less diagrammatic view in elevation of a cutoff saw incorporating a modified embodiment of the sensing and control means of this invention.

Referring now more particularly to the accompanying drawings, the numeral 5 designates generally a cutoff saw equipped with an automatic sensing and control device 6 which embodies the principles of this invention and which controls the return motion of the cutting head 7 of the machine.

The cutoff saw 5 is illustrated as being of the type that has as its cutting tool an endless saw band 8 trained around a pair of band wheels 9 in the manner of a band saw. The cutting head 7 thus comprises a rigid head frame 10 on which the band wheels are rotatably carried and which holds them in spaced coplanar relationship. It will be understood that one of the band wheels is rotatably driven by a motor (not shown).

The head frame 10 is mounted on a base or bed 12 of the machine for reciprocatory motion in cutting and return strokes. For purposes of illustration the connection 13 between the cutting head frame 10 and the machine bed 12 is shown as a hinged one, whereby the cutting head is constrained to swing in an arc in its cutting and return strokes. It will be recognized as the description proceeds that the automatic sensing and control device 6 could be applied without substantial modification to cutoff machines in which the cutting head is mounted on rails or the like for generally translatory reciprocation, either horizontally or vertically.

As is conventional, the cutting head is power actuated in its cutting and return strokes by means of a suitable motor 14, here shown as a hydraulic cylinder connected between the machine bed 12 and the cutting head frame 10 at points spaced from the axis of the hinged connection between them.

As will be evident from FIG. 1, the plane of the band wheels 9 on the cutting head is oblique to the direction of its reciprocating motion. The endless saw band 8 has a lower straight stretch between the band wheels, and the central portion 15 of this stretch, which is the cutting portion of the band, must of course be maintained with its surfaces parallel to the directions of cutting and return motion of the cutting head, so that it lies in a cutting plane in which it moves accurately edgewise as the head reciprocates. To hold the cutting portion of the blade in that orientation, with its toothed cutting edge 16 lowermost, a pair of saw guides 17 are rigidly secured to the cutting head frame 10. They engage the band at opposite ends of its cutting portion 15 and behind its cutting edge 16, imparting a twist to the blade in each of the portions thereof that extends between a band guide and its adjacent band wheel.

The machine bed 12 supports an elongated feed table 18 along which stock to be cut is advanced lengthwise in one direction to the cutting plane, and which comprises a series of freely rotatable rollers upon which the stock can ride.

In the present case the cutoff machine is assumed to have power actuated mechanism for effecting automatic indexing of the stock along the feed table, comprising a carriage 19 upon which a first vise 20 is mounted, and a second vise 21 is a fixed location adjacent to the cutting plane. The carriage 19 is reciprocable along the path of stock feed defined by the table 18 to carry its vise 20 in feeding and retracting motions toward and from the stationary vise 21.

The mechanism for actuating the carriage and the vises, and the control means for that mechanism, are well known and therefore are not shown in detail, although a general explanation of the control means is given hereinafter.

In general, the carriage and vises are operated by actuators (not shown) which are usually in the nature of hydraulic cylinders but which could be pneumatic or electric drives. The limit positions of the carriage are defined by trip switches (not shown) or the like that are adjustable along the path of its reciprocation. When the carriage reaches its retracted limit position it actuates one trip switch that stops its further motion in the retracting direction and causes the vise 20 on the carriage to be actuated to a clamping position at which it grips the stock to be cut. At the completion of a cut, and after the cutting head has returned to a position clear of the stock, the carriage advances along the feed path, through a predetermined increment in the feed direction, with its vise 20 still gripping the stock to carry the stock along with it.

When the carriage has advanced through the predetermined feed distance, it actuates its other cooperating trip switch. In response to such switch actuation the control means for the machine effects, in rapid succession, a termination of carriage motion in the feed direction, actuation of the stationary vise 21 from an open to a clamping position, movement of the cutting head in its cutting direction, actuation of the carriage mounted vise 20 to an open position to release its grip on the stock, and return motion of the carriage to its retracted limit position. The control means causes the stationary vise 21 to retain its grip on the stock through the cutting stroke of the cutting head and until just before the carriage begins to advance in its feed motion.

The sensing and control device 6 of this invention is operatively associated with the control means for the machine, as described hereinafter, and comprises a sensing element 26 that is responsive to the presence of stock. The sensing element is carried by the cutting head, or is otherwise constrained to move in unison with the cutting head, and is located in a zone near the cutting plane and along the path of stock feed that is defined by the feed table 18. The sensing element extends across said path and is arranged to be in a normal condition when there is no danger that stock in its zone will collide with the cutting head. When there is such danger, the sensing element responds to the presence of stock in its zone 'by causing the device 6 to issue an output that effects return motion of the cutting head and can also be utilized to prevent feeding advance of the carriage 19.

The sensing and control device is effectively disconnected from the control means for the machine during motion of the cutting head in its cutting direction, but is brought into cooperation with the control means at the conclusion of the cut, so that its automatic functioning causes return motion of the cutting head to continue until the blade is just clear of the stock.

In a machine having automatic stock feed, as described above, the zone in which the sensing element is located should be ahead of (i.e., upstream from) the cutting tool relative to the direction of stock advance, so that if a fresh piece of stock is being advanced toward the cutting plane and the cutting head is not in a position to clear it, the sensing element can detect the stock well before it collides with the cutting tool and its output can be utilized to halt the feed carriage as well as to effect return motion of the cutting head.

In order to accommodate stock of any and all shapes in cross section, the sensing element 26 is preferably arranged to respond to the presence of stock anywhere along a straight line which extends across the path of stock advance and which is parallel to the cutting edge 16 of the blade. That sensing line moves with the cutting head and is so located with respect to the cutting head as to be always spaced from the feed path by a distance which is preferably slightly less (but in any event no greater) than the distance from said path to the cutting edge of the blade. This is to'say that the sensing line just mentioned is slightly behind the cutting edge of the blade as the cutting head moves in its return direction, to insure that the cutting head will clear the stock with a reasonable margin of safety.

In the embodiment of the invention illustrated in FIG. 11 the sensing element 26 comprises a photoelectric cell 30 in cooperation with a light source 31, both mounted on the cutting head and so positioned thereon as to be at opposite sides of the path of stock advance. The light source and photoelectric cell of course face one another, and are provided with suitable lenses whereby light from the source is rather sharply focused upon the photoelectric cell.

The light source and photoelectric cell have their axes upon the straight sensing line described above, so that stock advancing along the feed path will come between them if the cutting head is in a position such that it will not clear the stock. It will be understood that the cell 31 is suitably connected with the control means for the machine in such a manner that interruption of the light falling upon the cell causes it to impose upon the control means an output such that the cutting head moves in its return direction and stock advance is temporarily halted. When the full light from the light source falls upon the cell, it of course cooperates with the control means to terminate return motion of the cutting head and to initiate or continue stock advance.

Since the photoelectric cell 30 can be affected by dirt and by light from sources other than its normal light source 31, the embodiment of the invention illustrated in FIGS. 1-10 is preferred in many cases. In this embodiment the sensing element 26 comprises a fairly rigid lever 35 having a front arm 36 that has the shape of a slender, elongated blade or wand and serves as a feeler, and a rear arm 37 that cooperates with a two position switch 38.

The lever is mounted on the cutting head for bodily movement therewith and for swinging motion in the directions of cutting head reciprocation by which its front arm or feeler 36 is carried to and from a normal position in which its straight bottom edge 39 extends along the sensing line described above. Preferably the lever is also swingable to and from its normal position in directions parallel to the path of stock advance. Its swinging motion in the directions of cutting head reciprocation enables it to respond to the presence of stock already at the cutting plane; by reason of its swinging motion in directions parallel to the feed path it can sense and respond to the front end of a fresh length of stock being advanced towards the cutting plane.

As hereinafter described, the lever is yieldingly biased towards its normal position, the biasing forces upon it being such as to urge its front arm in the direction of cutting motion of the head and in the direction opposite to that of stock feeding advance.

Both the lever 35 and the switch 38 are carried on a bracket 40 that is fixed on the cutting head frame 10 at a location thereon that is always spaced to one side of the stock feed path. To an upright wall of the bracket there is fixed a block 41 in which is journalled a generally upright pin 42 that provides the pivot about which the lever swings in directions parallel to the path of stock feed. A downwardly bifurcated, channel-like yoke 43 is fixed to the lower end of the pin 42, and the medial fulcrum portion of the lever 35 is confined between the legs or channels of that yoke so as to be constrained to swing therewith about the axis of the pin 42. For its swinging motion in the directions of cutting head movement the lever 35 has a pivotal connection with the yoke 43 provided by a horizontal pin 44 which bridges the legs of the yoke and extends through the fulcrum portion of the lever, and which has its axis intersecting that of the upright pin 42.

The upright pin 42 projects a distance above the fixed block 41 in which it is journalled, and a radial arm 45 is anchored to it just above the block. The arm 45 overlies both the block 41 and a thrust bearing 46 which is confined between the arm and the block, and the arm thus serves to confine the pin 42 against downward displacement. The arm 45 also serves to transmit to the upright pin 42 a torsional biasing force exerted by a spring 48 that has its coils embraching the upper end portion of said pin and has one of its ends anchored to the arm and its other end anchored to the fixed block 411. The spring 48 urges the lever 35 in the direction to swing its front feeler arm 36 oppositely to the direction of stock feed advance. A set screw 49 in the radial arm 45 engages the upright wall of the bracket to limit swinging of the lever 35 in response to the biasing force of the spring 43 and is adjusted to establish the lever in the above described normal position in which the straight bottom edge of its feeler 36 is parallel with the cutting edge MS of the saw blade.

One end portion of the horizontal pin 44 projects outwardly beyond one side of the yoke 43 to pilot the coils of another torsion spring 51 that has its opposite ends respectively connected with the yoke and with the lever. The biasing force exerted by the spring 51 tends to swing the feeler arm of the lever in the cutting direction of the head, in this case downwardly. Motion of the lever beyond its normal position, in response to such bias, is prevented by a set screw 52 that is threaded into the rear part of the yoke and engages an upper surface on the rear arm 37 of the lever.

The switch 38 has a pushbutton actuator 53 with limited travel between its extended and depressed positions. It is mounted on the bracket 40 with its actuator extending downwardly toward the rear arm 37 of the lever 35.

A motion transmitting connection between the lever 35 and the switch 38, comprising a leaf spring 54, causes any motion of the lever to or from its normal position to effect motion of the switch actuator 53 to one or the other of its defined positions. One end 55 of the leaf spring has a fixed connection with the bracket 40, while its other free end portion is formed as a shelflike flange 56 that extends over the rear arm 37 of the lever and beneath the switch actuator, substantially normal to the axis of the switch actuator. In the normal position of the flange 56, to which it is lightly biased by flexure of the leaf spring, the flange allows the switch actuator to assume its extended position; but the flexing bias of the leaf spring can be overcome by the biasing forces which the torsion springs 48 and 51 exert upon the lever 35, and when the lever is in its normal position its rear arm maintains the flange 56 in a position in which the switch actuator is fully depressed. Adjacent to its flange 56 the leaf spring has an inclined portion 57 that extends obliquely to said flange, and the rear arm 37 of the lever has a correspondingly inclined shoulder portion 58 that bears against said inclined portion of the leaf spring when the lever is in its normal position. Since these inclined portions on the leaf spring and on the lever are oblique to both of the axes about which the lever can swing, any movement of the lever out of its normal position will pennit the leaf spring to relax and flex its flange portion downwardly so that the switch actuator can move to its extended position, and movement of the lever to its normal position from any direction cams the leaf spring into depressing engagement with the actuator.

FIG. illustrates rather generally and diagrammatically the principal elements of the control means for the cutoff machine and the manner in which the switch 38 of the sensing and control device 6 is connected therewith. A selector control 59 determines whether the machine is operating in the cutting phase of its cycle or in that phase of its cycle in which the cutting head makes its return stroke and the carriage advances for stock feed. While the selector control is illustrated, for simplicity, as a double throw switch, it will be understood that it is actually a somewhat more complex mechanism which may comprise relays or the like connected with the trip switches that are actuated by the stock feed carriage at the predetermined limits of its instrumentalities for effecting properly coordinated actuation of the stationary vise 21 to its stock gripping condition, the carriage mounted vise 22 to its stock releasing condition, the carriage to the limit of its retracting motion, and the cutting head through its cutting stroke. Note that the sensing and control device 6 is not in the circuit just described, and therefore that device does not cause any interference with motion of the cutting head in its cutting stroke, even though the lever 35 is held out of its normal position by its engagement with the stock.

The selector control 59 is placed in its other condition by the trip switch 60 that is thrown when the cutting head reaches the end of its stroke. In said other condition the selector control establishes a circuit that includes the switch 38 of the sensing and control device 6, as well as known instrumentalities for coordinating motion, and also connected with a trip switch that is actuated by the cutting head at the completion of its cutting stroke and with suitable synchronizing mechanism that coordinates the movements of the various actuators. Since the various instrumentalities and connections that comprise the control means are known, they are merely indicated in the diagram by appropriately designated blocks.

When the selector control 59 is in the condition for the cutting phase of the machine cycle, in which it is illustrated in FIG. 10, it establishes a circuit that includes feed advance motion of the carriage, actuation of the vises 20 and 21, and return movement of the cutting head. At the conclusion of the first cut through a length of stock, the feeler arm 36 of the lever 35 will of course be engaged with the stock and will be held out of its normal position thereby, so that the switch 38 is in the position in which its output effects return motion of the cutting head but prevents the carriage actuating means from being energized. When the cutting head, in its return motion, has reached a position just clear of the stock, the lever 35 will assume its normal position, actuating the switch 38 to its other position in which it produces an output that effects feed advance of the carriage while motion of the cutting head is prevented.

FIG. 6 illustrates how the control device of this invention controls return motion of the cutting head so that such motion stops with the blade well clear of the stock, irrespective of the shape or size of the stock. Preferably the control means is arranged to cause the head to overtravel very slightly, so that the feeler 36 as well as the cutting blade will be clear of the stock to assure that the advancing stock will not drag the feeler out of its normal position.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides automatic means in a cutoff saw for sensing the presence of stock in or near the cutting zone, and for so controlling motion of the cutting head of the machine in its return direction as to assure that the cutting head will not undergo any unnecessary movement beyond that actually needed to position it clear of the stock. It will also be apparent that in a cutoff saw having automatic stock feed, the sensing and control device of this invention can prevent stock advance until the cutting head is clear of any danger of being struck by the advancing stock.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

1. A cutoff saw having a cutting head with a power driven blade having a cutting stretch that lies in a defined cutting plane, means defining a feed path generally normal to said cutting plane and along which stock to be cut can be fed to and through said cutting plane, said cutting head being mounted for movement to carry the cutting stretch of its blade edgewise in said cutting plane, and across said feed path in opposite cutting and return directions, power driven actuating means for moving the cutting head in said directions, and control means for said actuating means having selectable cutting and return conditions to provide, respectively, for movement of the cutting head in said cutting direction and said return direction, said cutoff saw being characterized by means for automatically so controlling motion of the cutting head in its return direction as to prevent such motion from continuing beyond the point at which the cutting stretch of the blade is clear of the path of stock being fed to the cutting plane, said last named means comprising:

A. stock sensing means constrained to move with the cutting head and to detect the presence of stock in a zone which is fixed with respect to the cutting head and is near the cutting plane and upstream therefrom with respect to said feed path;

B. output producing means responsive to the stock sensing means and operable to produce an output during movement of the cutting head and the said zone in the return direction as soon as the stock sensing means moving with the cutting head no longer detects the presence of stock in said zone; and

C. means so connecting said output producing means with said control means that in response to the production of said output return movement of the cutting head stops.

2. The cutoff saw of claim 1, further characterized in that with the cutting head in a position at which the cutting stretch of its blade is in the path of stock being fed to the cutting plane, the stock sensing means detects advance of stock beyond a point spaced a predetermined distance from the cutting plane wherein upon detection by the stock sensing means of advance of the stock beyond said point, said output producing means produces another output that is different from the aforesaid output; and wherein the connection of said output producing means with the control means is such that in response to said other output return movement of the cutting head to carry the cutting stretch of its blade out of the path of the advancing stock is effected.

3. The cutoff saw of claim 2, further characterized by: power means for advancing stock along the feed path;

and means operatively connecting said power means with the control means and through which the control means renders said power means inoperative concomitantly with the production of said other output.

4. The cutoff saw of claim 1, wherein said stock sensing means comprises:

a photo-responsive cell and means providing a light source arranged to direct a beam of light towards the photo-responsive cell, the light source and the photo-responsive cell being located at opposite sides of said feed path so that stock in said zone interrupts the light beam. and movement of the cutting head in the return direction beyond a point at which stock no longer interrupts the light beam effects production of said output by said output producing means.

5. The cutoff saw of claim 1, wherein said stock sensing means comprises:

A. a sensing arm which detects the presence of stock physically contacting it;

B. means mounting the sensing arm for swinging motion relative to the cutting head in said cutting and return directions and biasing it in V the cutting direction;

C. means cooperable with the sensing arm to define a normal position of swinging motion thereof towards which the sensing arm is biased and in which it extends along a line that is substantially parallel with the cutting stretch of the blade and nearer said feed path. than the cutting stretch so that the sensing arm occupies its normal position only when it is not in contact with stock and;

D. means operatively connecting the sensing arm with said output producing means and through which movement of the sensing arm to its normal position effects production of said output.

6. The cutoff saw of claim 5, wherein said means operatively connecting the sensing arm with the output producing means comprises:

A. a control element having an actuator for the output producing means, which actuator is movable back and forth between defined positions, in one of which positions said output is produced;

B. means holding the control element and the mounting means for the sensing arm in fixed relationship to one another and constraining them to move bodily in the cutting and return directions in unison with the cutting head; and

C. means providing a motion transmitting connection between the sensing arm and the actuator of the control element whereby said actuator is caused to occupy said one position when the sensing arm is in its normal position.

7. The cutoff saw of claim 5, wherein said zone in which thestocl; sensing means, in the form of said sensing arm is located, is spaced upstream from the cutting plane relative to said feed path,

and wherein the meansniointingthesensing arm also provides for swinging motion thereof to and from its normal position in directions parallel to the feed path and biases the arm in the direction opposite to that in which stock is advanced, so that the sensing arm will be displaced from its normal position by collision therewith of stock being advanced while the cutting head is in a position at which the cutting stretch of its blade is in the path of the advancing stock; wherein in response to displacement of the sensing arm by collision therewith of advancing stock, said output producing means produces another output which is different from the aforesaid output; and wherein the connection of said output producing means with the control means is such that in response to production of said other output return movement of the cutting head to carry the cutting stretch of its blade out of the path of the advancing stock is effected.

8. The cutoff saw of claim 7, further charac terized by: power means for advancing stock to the cutting plane; and means operatively connecting said power means with the control means and through which the control means renders said power means inoperative concomitantly with the production of said other output.

9. A cutoff saw having a cutting head with a power driven blade having a cutting stretch that lies in a defined cutting plane, means defining a feed path generally normal to said cutting plane and along which stock to be out can be fed to and through said cutting plane, said cutting head being mounted for movement to carry the cutting stretch of its blade edgewise in said cutting plane, and across said feed path in opposite cutting and return directions, power driven actuating means for moving the cutting head in said directions, and control means for said actuating means having selectable cutting and return conditions to provide, respectively, for movement of the cutting head in said cutting direction and in said return direction, said cutoff saw being characterized by automatic means for preventing stock advancing along said feed path from colliding with the cutting stretch of the blade and also preventing continuance of return movement of the cutting head beyond a point at which the cutting stretch of its blade is clear of advancing stock, said last mentioned means comprising:

A. a mechanical feeler;

B. mounting means for the feeler constrained to move in unison with the cutting head in said cutting and return directions, and by which the feeler is carried for bodily motion with the mounting means and for motion relative thereto in said cutting and return directions and in directions parallel with said feed path;

C. means biasing the feeler in said cutting direction and in the direction opposite stock advance;

D. means cooperating with said mounting means and said biasing means to define a normal position of the feeler towards which it is urged by the biasing means and in which at least a part of the feeler occupies a position near the cutting plane but upstream therefrom with respect to said feed path, in which normal position said part of the feeler extends transversely to said feed path, moves with the cutting head, and is spaced from said feed path by a distance no greater than the spacing therefrom of said cutting stretch; and

E. output producing means operatively associated with the control means and the feeler to effect motion of the cutting head in its return direction when stock being advanced displaces the feeler from its normal position, and to prevent return motion of the cutting head from continuing beyond said point at which the cutting stretch of the blade is clear of advancing stock in consequence of the feeler returning to its normal position.

10. A cutoff saw having a cutting head with a power driven blade having a cutting stretch that lies in a defined cutting plane, means defining a feed path generally normal to said cutting plane and along which stock to be cut can be fed to and through said cutting plane, said cutting head being mounted for movement to carry the cutting stretch of its blade edgewise in said cutting plane, and across said feed path in opposite cutting and return directions, power driven actuating means for moving the cutting head in said directions, and control means for said actuating means having selectable cutting and return conditions to provide, respectively, for movement of the cutting head in said cutting direction and in said return direction, said cutoff saw being characterized by automatic means for preventing stock advancing along said feed path from colliding wi th the cutting stretch of the blade, and also preventing continuance of return movement of the cutting head beyond a point at which the cutting stretch of its blade is clear of advancing stock, said last mentioned means comprising:

A. sensing means for detecting the presence of stock in a zone directly upstream of the cutting plane with respect to said feed path and which zone extends along a line that is parallel with the cutting stretch of the blade and is spaced from the feed path by a distance not greater than the spacing therefrom of the cutting stretch of the blade, said sensing means comprising an output producing sensing element constrained to move with the cutting head and to produce an output in consequence of the sensing element detecting stock in said zone; and

B. means so connecting said sensing element with the control means as to cause the cutting head to be moved in its return direction only when said output is produced and the control means is in its return condition. 

1. A cUtoff saw having a base, means on the base defining a feed path along which stock to be cut can be advanced in one direction, a cutting head comprising a power driven blade with a portion which has a cutting edge and lies in a defined cutting plane that is generally normal to said path, said cutting head being mounted for movement to carry said blade portion edgewise in said cutting plane and across said path in opposite cutting and return directions, power actuating means for moving the cutting head in its said directions, and control means for said actuating means having selectable cutting and return conditions to provide, respectively, for movement of the cutting head in said cutting and return directions, said cutoff saw being characterized by means for automatically so controlling motion of the cutting head in its return direction as to prevent stock advancing along said path from colliding with the cutting head but also prevent return movement of the cutting head beyond the point at which it is clear of advancing stock, the last mentioned means comprising: A. stock sensing means constrained to move in the cutting and return directions in unison with the cutting head in a zone near the cutting plane and operative to produce one output when stock is present along a line in said zone which is transverse to said path and to the directions of cutting and return motion of the cutting head and which line moves with the cutting head so as to be at all times spaced from the feed path by a distance not greater than the spacing therefrom of said cutting edge, said stock sensing means being responsive to the absence of stock from along said line to produce a different output; and B. means so connecting the stock sensing means with the control means when the latter is in its return condition as to effect motion of the cutting head in its return direction in response to said one output and to prevent such motion of the cutting head in response to said different output.
 2. means providing a light source directed toward the photoresponsive cell, the light source and photoresponsive cell having their axes on said line and being located at opposite sides of said path so that the cell produces said first output when stock intervenes between it and the light source and produces said second output when there is no stock between it and the light source.
 2. The cutoff saw of claim 1, further characterized by: said stock sensing means comprising
 2. means mounting the sensing arm for swinging motion in said cutting and return directions and biasing it in the cutting direction;
 2. moves with the cutting head so as to be at all times spaced from the feed path by a distance not greater than the spacing therefrom of said cutting edge, said means comprising an output producing sensing element constrained to move in unison with the cutting head and at least a part of which is normally located on said line to respond to the presence of stock therealong by producing an output; and B. means so connecting said sensing element with the control means as to cause the cutting head to be moved in its return direction only when said output is produced and the control means is in its return condition.
 2. means operatively connecting said power means with the control means and with the stock sensing means for rendering the power means inoperative in response to said one output and operative in response to said different output.
 3. means cooperable with the sensing arm to define a normal position of swinging motion thereof toward which the sensing arm is biased and in which it extends along said line;
 3. The cutoff saw of claim 1, further characterized by said stock sensing means comprising:
 4. The cutoff saw of claim 3, wherein said zone in which the stock sensing means is located is spaced upstream from the cutting plane relative to said direction in which stock is advanced, further characterized by: said means mounting the sensing arm also providing for swinging motion thereof to and From its normal position in directions parallel to the feed path, and biasing the arm in the direction opposite to that in which stock is advanced.
 4. a control element having an actuator movable back and forth between defined positions at which said outputs are respectively produced;
 5. means holding the control element and the mounting means for the sensing arm in a fixed relation to one another and constraining them to move bodily in the cutting and return directions in unison with the cutting head; and
 5. The cutoff saw of claim 4, further characterized by:
 6. A cutoff saw having a base, means on the base defining a feed path along which stock to be cut can be advanced in one direction, a cutting head comprising a power driven blade with a portion which has a cutting edge and lies in a defined cutting plane that is generally normal to said path, said cutting head being mounted for movement to carry said blade portion edgewise in said cutting plane and across said path in opposite cutting and return directions, power actuating means for moving the cutting head in its said directions, and control means for said actuating means having selectable cutting and return conditions to provide, respectively, for movement of the cutting head in said cutting and return directions, said cutoff saw being characterized by automatic means for so controlling motion of the cutting head in its return direction as to prevent stock advancing along said path from colliding with the cutting head but also prevent return movement of the cutting head beyond the point at which it is clear of advancing stock, the last mentioned means comprising: A. a mechanical feeler; B. mounting means for the feeler constrained to move in unison with the cutting head in said cutting and return directions and by which the feeler is carried for bodily motion with the mounting means and for motion relative thereto in said cutting and return directions; C. means biasing the feeler in said cutting direction; D. means cooperating with said mounting means and said biasing means to define a normal position of the feeler towards which it is urged by the biasing means and in which at least a part of the feeler lies on a line near the cutting plane, which line extends transversely to said path and to said cutting and return directions, moves with the cutting head, and is spaced from said path by a distance no greater than the spacing therefrom of said cutting edge; and E. output producing means operatively associated with the control means when it is in its return condition and operatively associated with the feeler to respond to its position and by which one output is produced when the feeler is out of its normal position that effects motion of the cutting head in its return direction and by which another output is produced when the feeler is in its normal position that prevents such motion of the cutting head.
 6. means providing a motion transmitting connection between the sensing arm and the actuator of the control element whereby said actuator is caused to occupy one of its said positions when the sensing arm is in its normal position and to occupy the other of its said positions when the sensing arm is out of its normal position.
 7. A cutoff saw having a base, means on the base defining a feed path along which stock to be cut can be advanced in one direction, a cutting head comprising a power driven blade with a portion which has a cutting edge and lies in a defined cutting plane that is generally normal to said path, said cutting head being mounted for movement to carry said blade portion edgewise in said cutting plane and across said path in opposite cutting and return directions, power actuating means for moving the cutting head in its said directions, and control means for said actuating means having selectable cutting and return conditions to provide, respectively, for movement of the cutting head in said cutting and return directions, said cutoff saw being characterized by automatic means for so controlling motion of the cutting head in its return direction as to prevent stock advancing along said path from colliding with the cutting head but also prevent return movement of the cutting head and beyond the point at which it is clear of advancing stock, the last mentioned means comprising: A. means for sensing the presence of stoCk along a line near the cutting plane, which line 